I often wondered whether something like that could be done here, in YUL. There are parallel runways as well, and I suppose that doing so could shave a few minutes from the transatlantic flights, on low wind days.

So, is it practical? When is it done? And why is it not done more often?

It happens at LAX nightly for the noise abatement procedures. It's pretty cool. They take off on the 25s and land on the 06s, so everything is out over the ocean. I was jumpseating on a flight where we were the first to switch to land eastbound, and there were still some a/c lining up in the opposite direction as we were lining up. Of course we were much further out to give them room to vacate the runway, but it was really cool looking out at aircraft directly opposing you for the same runway.

Aside from the most obvious reason (wind), I believe all ATC facilities operate in accordance with pre-established procedures and traffic "flows" which are developed with safety taking the top priority, and convenience coming in second.

For example at my airport, controllers use a "North flow" or "South flow" depending on the wind (conditions are rarely completely calm) and even though we have intersecting runways, I'm sure that larger airports with parallel runways operate on the same principles. The idea (as I understand it) is to keep everyone moving in the same general direction; this helps controllers organize & coordinate everyone much easier, especially when traffic picks up. Let's say that you are using opposing runway directions for arrivals and departures, and all of the sudden a storm front moves in and the wind starts gusting; if you are using opposing runway directions for arrivals and departures it might add quite a bit to your workload to re-arrange everyone to use the same runway directions.

Another safety concern would relate to missed approaches & go-arounds; by having arrivals approaching in the opposite direction of departures, you decrease the margin of safety if (for example) a pilot mistakenly turns the wrong direction on a go-around or missed approach (and into the path of an aircraft on climbout). The same could be true for a departure that encounters an emergency on takeoff/climbout. These dangers would only be magnified during operations in poor visibility/low ceilings.

There is also the issue of many airports which have only certain approaches on certain runways (ILS is a common example)... that would complicate things as well.

Finally, the whole idea of using opposing runways for arrivals & departures is pretty 'nonstandard.' As time has proven again and again, standardization (especially when it comes to procedures) is the way to go as far as aviation is concerned.

Well, when the winds shift, something's gotta give... I'm sure ATC lets someone already lined up for takeoff at a runway continue even when they switch directions on the field.

At ELP, WN usually tries to depart on the runway that will result in the shortest ground time (wind permitting, of course). I have seen WN depart 8R plenty of times when the ATIS said "Landing and departing Runway 26L". If the controller says yes, and they can space it, they will allow someone to go against the flow.

As an instrument student and pilot, I have shot the ILS (always to a missed approach, though) several times where we are going against the traffic flow. If an airfield only has an ILS on one runway, and traffic is departing and landing the other way, the only other choice is not to shoot the ILS. Controllers are usually pretty accomidating, although they may insist on extra vigilance or sidestepping the centerline on the missed approach... If you have to do it to a full stop, they will probably ask you to circle to land (if it's allowed on the approach).

Thanks for all those informations. It mostly goes along the lines I had figured, or the bits I knew. Yet, I somehow regret that our airport never seems to be on the quick side, when there is innovation around. Or, if it is, I never hear about it. I feel that Dorval, being a moderately busy airport, could be a very interesting field of experimentation... RNP, continuous descent (which is probably more or less a given here, because there is not much waiting), ecoflights...

... Except, maybe, for that procedure (of which I read about in A.net) requiring planes taking-off eastward to turn over the motorway giong north, instead of overflying populated areas... A procedure AC pilots could generally do easily, but which was less obvious for foreigners.

Back to my own topic: when I see European-bound airplanes taking-off over the west-island, in the opposite direction of their flight for relatively so long, I always wonder why they do not turn any earlier, over the lake... Or take-off in opposite direction.

There is something lke 1km separation between the runways at SYD, much greater than the separation at places like SFO & DFW, combined with a threshold displacement of approx 2.4km from North dir and about half that from the South, safety margins are just fine.
Indeed given those threshold displacements one could almost run SODPROPS* from a single (longer) runway... but wouldn't!

Quoting KELPkid (Reply 4):At ELP, WN usually tries to depart on the runway that will result in the shortest ground time (wind permitting, of course). I have seen WN depart 8R plenty of times when the ATIS said "Landing and departing Runway 26L".

WN does this at MSY all the time too, they will ask for 28 departures when traffic is landing on 10 (same runway). If the controller can fit them in between arrivals, they will let them do it.

Pretty common at night in RDU when the cargo heavies leave. If the wind is calm they request 23R departures, very close to the cargo ramps. I have seen this done with GA aircraft on approach to 5R. Kind of funny to hear a pilot's reply when their traffic is a heavy MD-11, opposite direction, off the parallel.

Not completely sure what SODROPS stands for, but looking at the map I would presume that an aircraft can't be leaving the ground if another is approaching the other runway. But once one of the aircraft turns away and has an adequate separation, then there are no further restrictions.